For stimulation of the right ventricle, the implantation of a lead through the right peripheral venous network typically suffices. However, to stimulate the left ventricle, the situation is more complex and the solution most often adopted is to introduce a lead into the coronary system via the right atrium and the coronary sinus ostium. Such a lead—which can be described as an endocardiac lead, but not as an endocardial lead—is described, e.g., in EP 0993840 A1 and its counterpart U.S. Pat. No. 6,385,492 (both assigned to Sorin CRM S.A.S., previously known as ELA Medical), and in the commercial product marketed under the name Situs LV by Sorin CRM, Clamart, France.
This implantation technique is not always feasible, however, especially when the conformation of the coronary sinus is too rugged, or when the patient has too much thrombosis. Indeed, the precise positioning of the electrode or electrodes to stimulate the left ventricle through the myocardium wall is a critical parameter, and it is not always possible to obtain a satisfactory configuration of the stimulation site.
Another known technique is to stimulate the left ventricle by applying stimulation pulses to the ventricular septum wall (also known as the interventricular septum), using a lead introduced into the right ventricle. One such stimulation technique of the left ventricle by a lead introduced into the right ventricle is described, e.g., in EP 1428550 A1 (De Bellis/P.A. SpA & M).
The U.S. Pat. No. 5,728,140 A also discloses a technique of left ventricular transeptal stimulation, without introduction of an electrode into the left cavity. Specifically, this device includes implanting a screw electrode penetrating the right septum wall, but whose length is slightly less than the thickness of the wall at the location of the stimulation site, so that the end of the screw approaches the left septal wall without crossing it.
If it is desirable to stimulate directly the left ventricle by an endocardial approach, the only techniques proposed so far are to drill a hole in the interatrial or interventricular septum, and then to introduce a lead through the septum until it comes into contact with a point of the left ventricle wall, where it is then anchored (e.g., by a fixation screw). The pacing pulses are applied directly to this selected endocardial site in the left ventricle.
This procedure, as currently implemented, however, has high operative risks, including risks of accidental perforation of the aorta, or dissection of the walls of the right atrium by a sudden rotational movement of the needle used for piercing the septum. Another risk of this technique is that of an air embolism, because the opening element in the left ventricle is a hollow catheter. To avoid this risk, it is imperative to take many precautions when handling hemostatic valves, to comply with procedures for purging the equipment, etc. However, given the highly invasive nature of this procedure, uncertainties remain about the behavior in the long term in the arterial circulation, which involves anticoagulation medication to prevent postoperatively thromboembolism. Finally, this technique virtually excludes any subsequent extraction of the lead, given the excessive risks that would be incurred at the crossing of the septum.
In any event, this technique is very difficult to implement and requires great skill of the practitioner who must, in order to cross the septum, always ensure perfect positioning of the needle for piercing on the wall of the septum, the crossing of the septum having to be undertaken only if there is no doubt about the position of the needle. Specific drilling kits also have been developed for this purpose, such as that described in EP 1516644 A1 and its counterpart U.S. Pat. No. 7,620,457 (both assigned to Sorin CRM S.A.S., previously known as ELA Medical).
The disadvantages mentioned above are also found in the system as is described in WO 2008/058265 A2. This document proposes to use as “left ventricular electrode” an element, introduced into a screw catheter, comprising a pointed end and provided with a harpoon-shaped tip designed to provide an anchoring point in the left wall cavity. This electrode is activated by a pusher introduced into the catheter, so as to push the tip through the septum and then deploy the electrode in the left ventricle. The catheter is then screwed to the wall of the septum, on the right side.
The assembly described in this document requires very difficult maneuvers for implantation, very different from what practitioners are used to. Its use is also very traumatic to the tissues, for the septum as well as for the left ventricular cavity, given the necessarily large diameter of the three elements telescopically nested into each other (catheter, deployable electrode and pusher). The implantation is of course not reversible, due to the harpoon-shaped tip and to the large diameter of the hole made in the septum, which could not close naturally in case of withdrawal. In addition, the surface area of the stimulation is relatively high, which leads to poor electrical performances and to high power consumption.